Conventionally, a scroll compressor as an example of a rotary compressor to compress a gas refrigerant in a refrigerating cycle has been used. The scroll compressor includes a fixed scroll and an orbiting scroll that have involute wraps engaged with each other in a casing. The fixed scroll is fixed in the casing and the orbiting scroll is coupled to an eccentric portion of a drive shaft (crank shaft). Further, the drive shaft is supported at the casing through a bearing. In the scroll compressor, the orbiting scroll just revolves orbitally to the fixed scroll without rotating on its own axis, thereby contracting a compression chamber formed between the wraps of both scrolls to compress a gas such as the refrigerant.
In general, such scroll compressor adopts lubricating structure in which a refrigerating machine oil collected in an oil reservoir in the casing is supplied to a sliding surface constituted between the both scrolls, a sliding face Constituted between the drive shaft and the bearing and the like through a main oil-supply passage formed in the drive shaft. For example, certain structure is disclosed in Japanese Laid-Open Patent Publication No. 8-261177, in which an oil reservoir is formed at a portion in a casing whose pressure is high, and a sliding surface constituted between both scrolls is connected to a suction side of a compressing mechanism so as to make the sliding surface a relatively low pressure, so that a refrigerating machine oil is supplied to the above sliding surface by pressure-differential pump structure that makes use of pressure differential between high-level pressure and low-level pressure.
Further, in the scroll compressor disclosed in the above publication, a bearing-portion oil-supply passage is formed in a drive shaft, which branches off from a main oil-supply passage and then connects with a sliding face constituted between the drive shaft and the bearing, and a spiral groove is formed at an inner peripheral face of the bearing, so that the refrigerating machine oil in the main oil-supply passage is supplied to the above sliding face. This spiral groove is open to high-pressure space in the casing at the both end portions in the axis direction of the bearing. In this case, the refrigerating machine oil that has lubricated the sliding face flows out of the spiral groove and then returns to the oil reservoir through the space in the casing.
-Problem to be Solved-
The above-described structure, however, is capable of supplying the refrigerating machine oil to the sliding surface at the both scrolls and the sliding surface of the bearing by the pressure-differential pump function during its ordinary operation, but there is some possibility that lubrication of the sliding face at the bearing may become insufficient during its starting operation. The reason for this is considered as the following. That is, during the starting operation of compressor, the gas refrigerant providing high-pressure atmosphere in the casing flows back in the spiral groove toward the main oil-supply passage before the refrigerating machine oil in the oil reservoir is supplied to the sliding surface at the both scrolls by the pressure-differential pump function. Thereby, it becomes difficult to supply the refrigerating machine oil in the oil reservoir to the sliding face at the bearing, and the oil remaining at the sliding face during a halt of the operation is forced to flow back to the main oil-supply passage. Accordingly, the temperature of the bearing tends to rise excessively for lack of lubrication, and repeating of this state may deteriorate the reliability of bearing, and in some cases, this may cause seizure of drive shaft.
The present invention has been devised in view of the above problem, and an object of the present invention is to improve the reliability of bearing, in the rotary compressor that adopts oil supplying to bearing by the pressure-differential pump, by preventing gas flowing into a portion between the drive shaft and the bearing.